Muscle knots in the Brachialis are located deep in the front of the upper arm, underneath the biceps brachii. These muscle knots can refer pain to the front of the elbow, upper arm, and surprisingly to the base of the thumb and the web between the thumb and index finger, often mimicking thumb arthritis or carpal tunnel syndrome. You may feel aching, tingling, or weakness during elbow flexion tasks like lifting, gripping, or carrying heavy objects.